[PATCH net-next v3 1/4] page_pool: frag API support for 32-bit arch with 64-bit DMA

Yunsheng Lin
2023-06-09T13:20:06Z

Currently page_pool_alloc_frag() is not supported in 32-bit
arch with 64-bit DMA, which seems to be quite common, see
[1], which means driver may need to handle it when using
page_pool_alloc_frag() API.

In order to simplify the driver's work for supporting page
frag, this patch allows page_pool_alloc_frag() to call
page_pool_alloc_pages() to return a big page frag without
page splitting because of overlap issue between pp_frag_count
and dma_addr_upper in 'struct page' for those arches.

As page_pool_create() with PP_FLAG_PAGE_FRAG is supported in
32-bit arch with 64-bit DMA now, mlx5 calls page_pool_create()
with PP_FLAG_PAGE_FRAG and manipulate the page->pp_frag_count
directly using the page_pool_defrag_page(), so add a checking
for it to aoivd writing to page->pp_frag_count that may not
exist in some arch.

Note that it may aggravate truesize underestimate problem for
skb as there is no page splitting for those pages, if driver
need a accuate truesize, it may calculate that according to
frag size, page order and PAGE_POOL_DMA_USE_PP_FRAG_COUNT
being true or not. And we may provide a helper for that if it
turns out to be helpful.

1. https://lore.kernel.org/all/20211117075652.58299-1-linyunsheng@huawei.com/

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
CC: Lorenzo Bianconi <lorenzo@kernel.org>
CC: Alexander Duyck <alexander.duyck@gmail.com>
---
.../net/ethernet/mellanox/mlx5/core/en_main.c | 9 ++++
include/net/page_pool.h | 44 ++++++++++++++++---
net/core/page_pool.c | 18 ++------
3 files changed, 51 insertions(+), 20 deletions(-)

diff --git a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
index a7c526ee5024..cd4ac378cc63 100644
--- a/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
+++ b/drivers/net/ethernet/mellanox/mlx5/core/en_main.c
@@ -832,6 +832,15 @@ static int mlx5e_alloc_rq(struct mlx5e_params *params,
/* Create a page_pool and register it with rxq */
struct page_pool_params pp_params = { 0 };

+ /* Return error here to aoivd writing to page->pp_frag_count in
+ * mlx5e_page_release_fragmented() for page->pp_frag_count is not
+ * usable for arch with PAGE_POOL_DMA_USE_PP_FRAG_COUNT being true.
+ */
+ if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) {
+ err = -EINVAL;
+ goto err_free_by_rq_type;
+ }
+
pp_params.order = 0;
pp_params.flags = PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV | PP_FLAG_PAGE_FRAG;
pp_params.pool_size = pool_size;
diff --git a/include/net/page_pool.h b/include/net/page_pool.h
index 126f9e294389..5c7f7501f300 100644
--- a/include/net/page_pool.h
+++ b/include/net/page_pool.h
@@ -33,6 +33,7 @@
#include <linux/mm.h> /* Needed by ptr_ring */
#include <linux/ptr_ring.h>
#include <linux/dma-direction.h>
+#include <linux/dma-mapping.h>

#define PP_FLAG_DMA_MAP BIT(0) /* Should page_pool do the DMA
* map/unmap
@@ -50,6 +51,9 @@
PP_FLAG_DMA_SYNC_DEV |\
PP_FLAG_PAGE_FRAG)

+#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT \
+ (sizeof(dma_addr_t) > sizeof(unsigned long))
+
/*
* Fast allocation side cache array/stack
*
@@ -219,8 +223,33 @@ static inline struct page *page_pool_dev_alloc_pages(struct page_pool *pool)
return page_pool_alloc_pages(pool, gfp);
}

-struct page *page_pool_alloc_frag(struct page_pool *pool, unsigned int *offset,
- unsigned int size, gfp_t gfp);
+struct page *__page_pool_alloc_frag(struct page_pool *pool,
+ unsigned int *offset, unsigned int size,
+ gfp_t gfp);
+
+static inline struct page *page_pool_alloc_frag(struct page_pool *pool,
+ unsigned int *offset,
+ unsigned int size, gfp_t gfp)
+{
+ unsigned int max_size = PAGE_SIZE << pool->p.order;
+
+ size = ALIGN(size, dma_get_cache_alignment());
+
+ if (WARN_ON(!(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
+ size > max_size))
+ return NULL;
+
+ /* Don't allow page splitting and allocate one big frag
+ * for 32-bit arch with 64-bit DMA, corresponding to
+ * the checking in page_pool_is_last_frag().
+ */
+ if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT) {
+ *offset = 0;
+ return page_pool_alloc_pages(pool, gfp);
+ }
+
+ return __page_pool_alloc_frag(pool, offset, size, gfp);
+}

static inline struct page *page_pool_dev_alloc_frag(struct page_pool *pool,
unsigned int *offset,
@@ -322,8 +351,14 @@ static inline long page_pool_defrag_page(struct page *page, long nr)
static inline bool page_pool_is_last_frag(struct page_pool *pool,
struct page *page)
{
- /* If fragments aren't enabled or count is 0 we were the last user */
+ /* We assume we are the last frag user that is still holding
+ * on to the page if:
+ * 1. Fragments aren't enabled.
+ * 2. We are running in 32-bit arch with 64-bit DMA.
+ * 3. page_pool_defrag_page() indicate we are the last user.
+ */
return !(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
+ PAGE_POOL_DMA_USE_PP_FRAG_COUNT ||
(page_pool_defrag_page(page, 1) == 0);
}

@@ -357,9 +392,6 @@ static inline void page_pool_recycle_direct(struct page_pool *pool,
page_pool_put_full_page(pool, page, true);
}

-#define PAGE_POOL_DMA_USE_PP_FRAG_COUNT \
- (sizeof(dma_addr_t) > sizeof(unsigned long))
-
static inline dma_addr_t page_pool_get_dma_addr(struct page *page)
{
dma_addr_t ret = page->dma_addr;
diff --git a/net/core/page_pool.c b/net/core/page_pool.c
index a3e12a61d456..9c4118c62997 100644
--- a/net/core/page_pool.c
+++ b/net/core/page_pool.c
@@ -14,7 +14,6 @@
#include <net/xdp.h>

#include <linux/dma-direction.h>
-#include <linux/dma-mapping.h>
#include <linux/page-flags.h>
#include <linux/mm.h> /* for put_page() */
#include <linux/poison.h>
@@ -200,10 +199,6 @@ static int page_pool_init(struct page_pool *pool,
*/
}

- if (PAGE_POOL_DMA_USE_PP_FRAG_COUNT &&
- pool->p.flags & PP_FLAG_PAGE_FRAG)
- return -EINVAL;
-
#ifdef CONFIG_PAGE_POOL_STATS
pool->recycle_stats = alloc_percpu(struct page_pool_recycle_stats);
if (!pool->recycle_stats)
@@ -715,18 +710,13 @@ static void page_pool_free_frag(struct page_pool *pool)
page_pool_return_page(pool, page);
}

-struct page *page_pool_alloc_frag(struct page_pool *pool,
- unsigned int *offset,
- unsigned int size, gfp_t gfp)
+struct page *__page_pool_alloc_frag(struct page_pool *pool,
+ unsigned int *offset,
+ unsigned int size, gfp_t gfp)
{
unsigned int max_size = PAGE_SIZE << pool->p.order;
struct page *page = pool->frag_page;

- if (WARN_ON(!(pool->p.flags & PP_FLAG_PAGE_FRAG) ||
- size > max_size))
- return NULL;
-
- size = ALIGN(size, dma_get_cache_alignment());
*offset = pool->frag_offset;

if (page && *offset + size > max_size) {
@@ -759,7 +749,7 @@ struct page *page_pool_alloc_frag(struct page_pool *pool,
alloc_stat_inc(pool, fast);
return page;
}
-EXPORT_SYMBOL(page_pool_alloc_frag);
+EXPORT_SYMBOL(__page_pool_alloc_frag);

static void page_pool_empty_ring(struct page_pool *pool)
{
--
2.33.0